<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>标签</title>
    <style>
        .main {
            width: 500px;
            height: 500px;
            border: 1px solid black;
            margin: 100px auto;
            text-align: center;
            font: bold 25px Arial sans-serif;
        }
    </style>
</head>
<body>
<div class="main">
    <p class="item">if语句</p>
    {% if age > 18 %}
        <p class="item">您已经满了18岁，可以进入网吧</p>
    {% else %}
        <p class="item">未成年，禁止进入</p>
    {% endif %}
</div>

</body>
</html>